Synthesis and characterization of rectangular tetranuclear cluster complexes of molybdenum(II) by condensation of quadruply bonded dimers

Article abstract of DOI:10.1021/ic00135a069

Several new synthetic methods have been developed for preparation of the rectangular tetrameric cluster complexes Mo₄X₈L₄ (X = Cl, Br, I; L = neutral donor ligand). Mo₄Cl₈(CH₃OH)₄ is prepared efficiently from the dimer Mo₂Cl₄(PPh₃)₂(CH₃OH) ₂ and subsequently converted in good yield to Mo₄Cl₈(C₂H₅CN)₄ by reaction with propionitrile. Reaction of Mo₄Cl₈(C₂H₅CN)₄ with triphenylphosphine yields Mo₄Cl₈(PPh₃)₄, and with tetrahydrofuran the unstable Mo₄Cl₈(THF)₄ is afforded. The trialkylphosphine derivatives Mo₄Cl₈(PR₃)₄ (R = C₂H₅ or C₄H₉) may be obtained more conveniently in reactions between (a) K₄Mo₂Cl₈ + PR₃ (1:2 mole ratio), (b) Mo₂(O₂CCH₃)₄ + PR₃ + (CH₃)₃SiCl (1:2:4 mole ratio), (c) Mo₂(O₂CCH₃)₄ + PR₃ + AlCl₃ (1:2:2 mole ratio), or (d) Mo₂Cl₄(PR₃)₄ + Mo(CO)₆ (1:1 mole ratio). The Mo₄Br₈(P-n-Bu₃)₄ prepared by analogous methods exhibits properties closely related to the chloride derivative; Mo₄I₈(P-n-Bu₃)₄ however appears to consist of weakly coupled quadruply bonded dimers. The various compounds have been characterized by UV-visible, infrared, and Cl 2p photoelectron spectra which reflect the basic rectangular cluster structure known for Mo₄Cl₈(PEt₃)₄.